Low latency is necessary to provide a positive user experience for Voice over Internet Protocol (VoIP), Push-to-transmit over Cellular (PoC) and videophone application based services. According to the International Telecommunications Union (ITU), an intra-regional VoIP call, for example, a call within Africa, Europe, North America, etc., should experience single direction latency on the order of 150 msec. An inter-regional VoIP call should experience single direction latency on the order of 200-300 msec.
Hybrid Automatic Repeat reQuest (HARQ) is known generally. EGPRS currently existing within GSM enables HARQ by periodic polling. The polling mechanism, however, is a fundamental cause of latency. In section 10 of the GERAN Evolution Feasibility Study 45.912, ACK/NACK messages are enabled either through polling and/or continuous bi-directional data flow. Thus where there is no continuous bi-directional data flow, low latency can only be guaranteed by continuous polling. However, continuous polling is spectrally inefficient and does not allow seamless interoperability with legacy mobile stations. Currently, wireless communication network operators must disable HARQ completely or operate HARQ in a spectrally inefficient manner to support low latency applications such as voice over IP or real time video streaming.
For a mobile to mobile VoIP call, existing EGPRS protocols with Automatic Repeat Request (ARQ) have latency on the order of 420 msec for each uplink or downlink. This latency exceeds the 200-300 msec latency for an inter-regional VoIP call and is well beyond the 150 msec latency for an intra-regional VoIP call.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description and the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.